New submission from Mark Lundeberg:
Although -0.0 and +0.0 compare as equal using the == operator, they are
distinct floating point numbers and in some cases behave differently. (See more
information on the wikipedia article "Signed zero".) The distinction between
+0.0 and -0.0 is most important in complex arithmetic, for example it is
conventional and useful that sqrt(-1+0i) ==> +i and sqrt(-1-0i) ==> -i. Python
currently allows the floating point number -0.0 to be entered as a literal:
>>> -0.0
-0.0
Complex floating point numbers in python also can hold negative zero
components, as shown in their repr()
>>> -(1+0j)
(-1-0j)
However they cannot be input directly as literals; it is currently necessary to
use the above construction. Unfortunately the output of the repr() cannot be
used as a string literal to obtain the same number:
>>> (-1-0j)
(-1+0j)
except, in contrast:
>>> complex('-1-0j')
(-1-0j)
The literal -1-0j should yield a complex number with negative zero imaginary
part. Note also that complex literals with negative zero real parts have the
same bug, e.g. -0+1j is not the same as -(0-1j)
----------
components: Interpreter Core
messages: 256209
nosy: Mark Lundeberg
priority: normal
severity: normal
status: open
title: negative zero components are ignored in complex number literals
type: behavior
versions: Python 2.7, Python 3.4
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Python tracker <[email protected]>
<http://bugs.python.org/issue25839>
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